1. Field of the Invention
This invention relates to a strap tightener for tightening a strap to hold heavy loads under tension firmly in a given position. More particularly, this invention relates to a strap tightener in which a specific releasable tensioning and clasping mechanism for a flexible strap is incorporated to tie down heavy loads such as cargo containers and motor vehicles to fixing structures equipped, for example, on carrier vessels or carts for preventing arbitrary movement of such heavy loads while they are fastened.
2. Description of the Prior Art:
In the past, a variety of strap tightening or clasping devices were designed for securely holding cargo and the like objects in position with a strap element. However, these known strap tightening devices more or less accompany such disadvantages as unexpected release of tension while the device is being used, damage of strap elements. Further, the prior art devices require complicate mechanism. For example, the strap securing device disclosed in U.S. Pat. No. 2,852,827 comprises a frame 17 consisting of two spaced side plates and a handle 18 provided with a beam 22 and supported on a pivot 19 extending between the side plates to enable pivotal movement of the handle pivotably. A strap 11 enters in the device through the clearance formed below the pivot and extends around and underneath the pivot. When the handle 18 is moved from the open position to the closed or locked position, the mechanism of this device permits the beam to move around the pivot whereby the strap around the beam is squeezed around the pivot in such a manner that the outer strap around the pivot may clasp itself to the inner strap around the pivot. The device of this type is also seen in U.S. Pat. No. 3,099,055 where a strap tensioning device is disclosed which comprises a frame 15 and a handle 20 provided with a strap engaging beam 23 and pivotably supported on a pivot 19 and functions in the same manner as in the above mentioned strap securing device and in U.K. Pat. No. 966,133 where a buckle for connecting a strap to another strap is disclosed which comprises a body affording a pair of side rails 10, a frame 15 corresponding to the handle disclosed in the above mentioned U.S. patent, and a movable anchorage 25 corresponding to the strap engaging beam. The mechanism used in these devices requires a lock means. In the device disclosed in the firstly mentioned U.S. patent, for example, a combination of a latch 28 and a slot 29 is required to engage the handle firmly with the frame when the former is held in the closed position. Otherwise, the handle may be moved to the open or release position. Further, this mechanism has such a shortcoming that when the strap holding down cargo is loosened by shock or the like external force, the clasping force of the outer strap against the inner strap around the pivot is so weakened as to permit slippage of the cargo.
Another example of the known devices is seen in U.S. Pat. No. 2,710,436 where cargo tie-down equipment is disclosed which basically has the same structure as described above except that a toggle lever 27 of this equipment as provided with two beams (a roller pin 32 and a rigid pin 34) and the frame of this equipment is also provided with a cross pin 35. The device of this type succeeds in preventing loosening of the strap holding down cargo but, on the other hand, has such disadvantage wherein the path of the strap running through the pins becomes complicated and a combination of a locking pin and a slot is also required to secure the toggle lever in the closed position.
Further examples of the known devices are seen in U.S. Pat. Nos. 2,867,406; 3,050,799 and 4,054,971. The cargo tie-down equipment disclosed in U.S. Pat. No. 2,867,406 comprises as in the device disclosed in U.S. Pat. No. 2,852,827 a retainer 26 and a lever 20 rotatably supported on a second pin 25 and provided with a cross pin 18 as a beam and is characterized in that the lever is provided on a pivotal support 21 with a yoke 23. As compared with the mechanism used in U.S. Pat. Nos. 2,710,436 or 2,852,827, the mechanism used in this equipment has no need of using a lock means because the force acting in the reverse direction to the strap entering in the equipment is supported by the yoke 23, i.e. the lever 20 in place of the retainer, through the pivotal support 21 and because the force acting on the pivotal support is supported by the lever in the closed position. This mechanism is common to the tiedown buckle disclosed in U.S. Pat. No. 3,050,799 which comprises a buckle frame 13 and a lever 11 rotatably supported on a pin 12 and provided with a cross pin 20 as a beam. The clasping device disclosed in U.S. Pat. No. 4,054,971 comprises, as in the case of the equipment disclosed in U.S. Pat. No. 2,867,406, a body X and a lever means Y rotatably supported on a pin member 20 and provided with a stanchion 21 and is characterized in that the lever means is provided on a pin member 23 with a holder Z. The mechanism used in this device is basically equivalent to that used in the above mentioned cargo tiedown equipment and thus has no need of using a lock means, as the force acting in the reverse direction to the strap entering in the device is supported by the lever means through the pin member 23 and the force acting thereon is supported by the lever means in the closed position. A lock means is quite unnecessary in this mechanism but may be used for precaution as represented by a combination of a turn-button 28 and a handle portion 29 in the cargo tie-down equipment or a combination of a detent hole 26 and a projection 27 in the clasping device. The above equipment and devices have a merit of preventing unexpected release of tension, but are unsatisfactory in other aspects; a smooth operation cannot be expected in these devices and damage of a strap element cannot be prevented to a satisfactory degree. Accordingly, there is still a great demand in the field of transportation for developing a new type strap tightener in which the above mentioned drawbacks are all overcome.